Chemical beneficiation of phosphatic limestone and phosphate rock with α-hydroxysulfonic acids

ABSTRACT

A method of selectively extracting calcite and dolomite away from apatite in phosphate rock or phosphatic limestone wherein the phosphate rock or phosphatic limestone is treated with a mixture of sulfur dioxide, water, and a carbonyl compound. Solids are separated from the liquid phase. The solids consist principally of apatite admixed with clay, quartz, and other accessory minerals originally in the rock. The solids are heated to drive off adhering sulfur dioxide, water, and carbonyl. The liquid phase consists of carbonyl, water, sulfur dioxide, and magnesium and calcium ions. Heating this liquid preferentially precipitates CaSO 3 .1/2H 2  O. This solid is filtered off and the filtrate further heated to precipitate MgSO 3 .3H 2  O largely free of CaSO 3 .1/2H 2  O. All offgas and filtrate is returned to the process. Examination of extraction results shows that high temperature extraction favors dolomite extraction and low temperature extraction favors apatite extraction. Thus, operating at elevated temperature allows dolomite to be selectively extracted from the apatite in phosphate rock.



